Electric water pump

ABSTRACT

An electric water pump apparatus may include a body having a stator chamber and a rotor chamber therein, a stator having a hollow cylindrical shape and being disposed in the stator chamber and generating a magnetic field, wherein the stator fluidly insulates the stator chamber and the rotor chamber, a rotor disposed in the rotor chamber and enclosed by the stator, wherein the rotor is rotated by the magnetic field, and a pump cover connected to the body and forming a volute chamber therein, wherein the volute chamber and the rotor chamber are fluidly-communicated through a connecting hole formed to the body and a coolant is supplied to the rotor chamber through the connection hole, wherein the stator includes a stator groove formed in an inner circumference therein and the stator groove is fluid-connected to the rotor chamber and the volute chamber through the connection hole.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to Korean Patent Application No. 10-2009-0112236 filed on Nov. 19, 2009, the entire contents of which is incorporated herein for all purposes by this reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electric water pump. More particularly, the present invention relates to an electric water pump having improved performance and durability.

2. Description of Related Art

Generally, a water pump circulates coolant to an engine and a heater in order to cool the engine and heat a cabin. The coolant flowing out from the water pump circulates through and exchanges heat with the engine, the heater, or the radiator, and flows back in the water pump. Such a water pump is largely divided into a mechanical water pump and an electric water pump.

The mechanical water pump is connected to a pulley fixed to a crankshaft of the engine and is driven according to rotation of the crankshaft (i.e., rotation of the engine). Therefore, the coolant amount flowing out from the mechanical water pump is determined according to rotation speed of the engine. However, the coolant amount required in the heater and the radiator is a specific value regardless of the rotation speed of the engine. Therefore, the heater and the radiator do not operate normally in a region where the engine speed is slow, and in order to operate the heater and the radiator normally, the engine speed must be increased. However, if the engine speed is increased, fuel consumption of a vehicle also increases.

On the contrary, the electric water pump is driven by a motor controlled by a control apparatus. Therefore, the electric water pump can determines the coolant amount regardless of the rotation speed of the engine. Since components used in the electric water pump, however, are electrically operated, it is important for electrically operated components to have sufficient waterproof performance. If the components have sufficient waterproof performance, performance and durability of the electric water pump may also improve.

Currently, the number of vehicles having an electric water pump is tending to increase. Accordingly, various technologies for improving performance and durability of the electric water pump are being developed.

The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

BRIEF SUMMARY OF THE INVENTION

Various aspects of the present invention are directed to provide an electric water pump having advantages of improved performance and durability and to provide an electric water pump which minimizes magnetic flux leakage of a permanent magnet by optimizing a shape of a rotor core.

In an aspect of the present invention, the electric water pump apparatus may include a body having a hollow cylindrical shape and including a stator chamber and a rotor chamber therein, a stator having a hollow cylindrical shape and being disposed in the stator chamber and generating a magnetic field according to a control signal, wherein the stator fluidly insulates the stator chamber and the rotor chamber, a rotor disposed in the rotor chamber and enclosed by the stator, wherein the rotor is rotated by the magnetic field generated at the stator, and a pump cover connected to the body and forming a volute chamber therein, wherein the volute chamber and the rotor chamber are fluidly-communicated through a connecting hole formed to the body and a coolant having flowed into the volute chamber is supplied to the rotor chamber through the connection hole, wherein the stator includes a stator groove formed in an inner circumference therein and the stator groove is fluid-connected to the rotor chamber and the volute chamber through the connection hole.

The rotor core having a hollow cylindrical shape may include a coupling groove formed along an inner circumference in a length direction therein and the rotor core is splined to the shaft through the coupling groove.

The stator may include a stator core having a hollow cylindrical shape to receive the rotor therein and provided with the stator groove at an inner circumference thereof along a length direction, and a stator case mounted at both distal ends of the stator core, wherein the stator case is made of a bulk mold compound including a potassium family that has a low coefficient of contraction.

The stator case may be provided with a fixing groove and a driver providing the control signal is slidably and detachably coupled thereto.

The rotor may include a rotor core having a hollow cylindrical shape to receive a shaft therein, and provided with a plurality of recesses formed by a plurality of guiding protrusions formed at an exterior circumference thereof along a length direction, a plurality of permanent magnets respectively mounted in the plurality of recesses of the rotor core, a rotor cover mounted at both distal ends of the rotor core and the plurality of permanent magnets so as to fix the rotor core and the plurality of permanent magnets each other, and a rotor case enclosing an exterior circumference of the rotor core and the plurality of permanent magnets so as to fix the rotor core and the plurality of permanent magnet each other in a state that the rotor core and the plurality of permanent magnets are mounted at the rotor cover, wherein the rotor case may be made of a bulk mold compound including a potassium family that has a low coefficient of contraction.

The plurality of permanent magnets may be mounted in such a manner that N pole and S pole are alternatively disposed.

The rotor cover may be provided with a plurality of balance holes and rotational balance of the rotor may be kept by changing positions of the balance holes.

In addition, the stator case may be provided with a plurality of balance holes and rotational balance of the stator may be kept by changing positions of the balance holes.

The methods and apparatuses of the present invention have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description of the Invention, which together serve to explain certain principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an exemplary electric water pump according to the present invention.

FIG. 2 is a cross-sectional view taken along the line A-A in FIG. 1.

FIG. 3 is a perspective view showing a stator of an exemplary electric water pump according to the present invention.

FIG. 4 is a perspective view of a rotor cover used in an exemplary electric water pump according to the present invention.

FIG. 5 is a perspective view showing a shape of a rotor core used in an exemplary electric water pump according to the present invention.

FIG. 6 is a schematic diagram showing processes for mounting rotor covers to both ends of a rotor core and a permanent magnet in an exemplary electric water pump according to the present invention.

FIG. 7 is a schematic diagram showing processes for manufacturing a rotor used in an exemplary electric water pump according to the present invention.

It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment.

In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims.

An exemplary embodiment of the present invention will hereinafter be described in detail with reference to the accompanying drawings.

FIG. 1 is a perspective view of an electric water pump according to an exemplary embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along the line A-A in FIG. 1.

As shown in FIG. 1 and FIG. 2, an electric water pump 1 according to an exemplary embodiment of the present invention includes a pump cover 10, a body 30, a driver case 50, and a driver cover 70. The body 30 is engaged to a rear end of the pump cover 10 so as to form a volute chamber 16, the driver case 50 is engaged to a rear end of the body 30 so as to form a rotor chamber 38 and a stator chamber 42, and the driver cover 70 is engaged to a rear end of the driver case 50 so as to form a driver chamber 64.

In addition, an impeller 22 is mounted in the volute chamber 16, a rotor 200 (referring to FIG. 7) fixed to a shaft 82 is mounted in the rotor chamber 38, a stator 101 is mounted in the stator chamber 42, and a driver 80 is mounted in the driver chamber 64. The shaft 82 has a central axis x, and the rotor 200 as well as the shaft 82 rotate about the central axis x. The stator 101 is disposed coaxially with the central axis x of the shaft 82.

The pump cover 10 is provided with an inlet 12 at a front end portion thereof and an outlet 14 at a side portion thereof. Therefore, the coolant flows in the electric water pump 1 through the inlet 12, and the pressurized coolant in the electric water pump 1 flows out through the outlet 14. A slanted surface 18 is formed at a rear end portion of the inlet 12 of the pump cover 10, and a rear end portion 20 of the pump cover 10 is extended rearward from the slanted surface 18. The rear end portion 20 of the pump cover 10 is engaged to a cover mounting portion 44 of the body 30 by fixing means such as a bolt B. The slanted surface 18 is slanted with reference to the central axis x of the shaft 82, and an intersecting point P of lines extended from the slanted surface 18 is located on the central axis x of the shaft 82.

The volute chamber 16 for pressurizing the coolant is formed in the pump cover 10, and the impeller 22 for pressurizing and discharging the coolant through the outlet 14 is mounted in the volute chamber 16. The impeller 22 is fixed to a front end portion of the shaft 82 and rotates together with the shaft 82. For this purpose, a bolt hole 29 is formed at a middle portion of the impeller 22 and a thread is formed at an interior circumference of the bolt hole 29. Therefore, an impeller bolt 28 inserted in the bolt hole 29 is threaded to the front end portion of the shaft 82 such that the impeller 22 is fixed to the shaft 82. A washer w may be interposed between the impeller 22 and the impeller bolt 28.

The impeller 22 is provided with a confronting surface 26 corresponding to the slanted surface 18 at the front end portion thereof. Therefore, an intersecting point of lines extended from the confronting surface 26 is also positioned on the central axis x of the shaft 82. The coolant having flowed into the water pump 1 may be smoothly guided and performance of the water pump 1 may be improved as a consequence of disposing centers of the impeller 22 and the rotor 200 that are rotating elements of the water pump 1 and a center of the stator 101 that is a fixed element of the water pump 1 on the central axis x.

In addition, the impeller 22 is divided into a plurality of regions by a plurality of blades 24. The coolant having flowed into the plurality of regions is pressurized by rotation of the impeller 22.

The body 30 has a hollow cylindrical shape that is opened rearward, and is engaged to the rear end of the pump cover 10. The body 30 includes a front surface 32 forming the volute chamber 16 with the pump cover 10, the stator chamber 42 that is formed at an exterior circumferential portion of the body 30 and in which the stator 101 is mounted, and the rotor chamber 38 that is formed at an interior circumferential portion of the stator chamber 42 and in which the rotor 200 is mounted.

The front surface 32 of the body 30 is provided with the cover mounting portion 44, a first stator mounting surface 40, a first bearing mounting surface 48, and a penetration hole 34 formed sequentially from an exterior circumference to a center thereof.

The cover mounting portion 44 is engaged to the rear end portion 20 of the pump cover 10. Sealing means such as an O-ring O may be interposed between the cover mounting portion 44 and the rear end portion 20 in order to prevent leakage of the coolant from the volute chamber 16.

The first stator mounting surface 40 is protruded rearward from the front surface 32, and defines a boundary between the stator chamber 42 and the rotor chamber 38. In a state that the sealing means such as an O-ring O is mounted at the first stator mounting surface 40, the front end of the stator 101 is mounted at the first stator mounting surface 40.

The first bearing mounting surface 48 is protruded rearward from the front surface 32. A first bearing 94 is interposed between the first bearing mounting surface 48 and the front end portion of the shaft 82 in order to make the shaft 82 smoothly rotate and to prevent the shaft 82 from being inclined.

The penetration hole 34 is formed at a middle portion of the front surface 32 such that the front end portion of the shaft 82 is protruded to the volute chamber 16 through the penetration hole 34. The impeller 22 is fixed to the shaft 82 in the volute chamber 16. It is exemplarily described in this specification that the impeller 22 is fixed to the shaft 82 by the impeller bolt 28. However, the impeller 22 may be press-fitted to an exterior circumference of the shaft 82.

Meanwhile, a connecting hole 36 is formed at the front surface 32 between the first stator mounting surface 40 and the first bearing mounting surface 48. Therefore, the rotor chamber 38 is fluidly connected to the volute chamber 16. Heat generated at the shaft 82, the rotor 200, and the stator 101 by operation of the water pump 1 is cooled by the coolant flowing in and out through the connecting hole 36. Therefore, durability of the water pump 1 may improve. In addition, floating materials in the coolant are prevented from being accumulated in the rotor chamber 38.

The rotor chamber 38 is formed at a middle portion in the body 30. The shaft 82 and the rotor 200 are mounted in the rotor chamber 38.

A stepped portion 83, the diameter of which is larger than that of the other part, is formed at a middle portion of the shaft 82. According to an exemplary embodiment of the present invention, a hollow shaft 82 may be used. A spline portion (not shown) may be formed at an exterior circumference of the stepped portion 83 along the central axis x.

The rotor 200 is fixed on the stepped portion 83 of the shaft 82, and is formed in an unsymmetrical shape. Thrust is exerted on the shaft 82 toward the front surface 32 by the unsymmetrical shape of the rotor 200 and a pressure difference between the volute chamber 16 and the rotor chamber 38. The thrust generated at the shaft 82 pushes the shaft 82 toward the front surface 32. Thereby, the stepped portion 83 of the shaft 82 may be interfere and collide with the first bearing 94 and the first bearing 94 may be damaged, accordingly. In order to prevent interference and collision of the stepped portion 83 of the shaft 82 and the first bearing 94, a cup 100 is mounted between the stepped portion 83 of the shaft 82 and the first bearing 94. Such a cup 100 is made of an elastic rubber material, and relieves the thrust of the shaft 82 exerted to the first bearing 94.

Meanwhile, in a case that the cup 100 directly contacts the first bearing 94, the thrust of the shaft 82 exerted to the first bearing 94 can be relieved. However, rotation friction may be generated between the first bearing 94 and the cup 100 of a rubber material, and thereby performance of the water pump 1 may be deteriorated. Therefore, a thrust ring 98 is mounted between the cup 100 and the first bearing 94 in order to reduce the rotation friction between the first bearing 94 and the cup 100. That is, the cup 100 reduces the thrust of the shaft 82 and the thrust ring 98 reduces the rotation friction of the shaft 82. It is exemplarily described in this specification that a groove is formed at an exterior circumference of the cup 100 and the thrust ring 98 is mounted in the groove. However, a method for installing the thrust ring 98 to the cup 100 is not limited to the exemplary embodiment of the present invention. For example, a groove may be formed at a middle portion of the cup 100 and the thrust ring 98 may be mounted in this groove. Further, it is to be understood that any thrust ring 98 interposed between the cup 100 and the first bearing 94 may be included in the spirit of the present invention.

The rotor 200 includes a rotor core 86, a permanent magnet 88, a rotor cover 84, and a rotor case 90.

As shown in FIG. 2 and FIG. 5, the rotor core 86 has a hollow cylindrical shape and is fixed to the stepped portion 83 of the shaft 82 by press-fitting or welding, or is splined to the stepped portion 83 of the shaft 82. It is exemplarily described in this specification that the rotor core 86 is splined to the stepped portion 83 of the shaft 82. For this purpose, a coupling groove 204 is formed at an interior circumference of the rotor core 86 along the central axis x and is splined to the stepped portion 83.

A plurality of guiding protrusions 202 is formed at the exterior circumference of the rotor core 86 along the central axis x, and a plurality of recesses 203 is formed between the guiding protrusions 202 along the central axis x. In addition, the permanent magnets 88 are insertedly mounted in each recess 203. Therefore, the plurality of guiding protrusions 202 prevents the permanent magnet 88 from rotating. In addition, the plurality of guiding protrusions 202 does not cover both ends of the permanent magnet 88 so as to limit axial movement of the permanent magnet 88. If the guiding protrusion 202 covers both ends of the permanent magnet 88, magnetic flux generated by the permanent magnet 88 may leak. Such a leakage of the magnetic flux causes that the more and the larger permanent magnet 88 should be used. Therefore, size of the water pump 1 may increase. According to an exemplary embodiment of the present invention, the guiding protrusion 202, however, does not cover both ends of the permanent magnet 88, and thus leakage of the magnetic flux may be reduced. Therefore, sufficient capacity of the water pump 1 may be achieved without increasing the size of the water pump 1.

The permanent magnet 88 is mounted in the recess 203 formed at the exterior circumference of the rotor core 86. The permanent magnet 88 includes N pole and S pole and is mounted in such a manner that the N pole and the S pole are alternately disposed.

As shown in FIG. 2 and FIG. 4, a pair of rotor covers 84 is mounted at both ends of the rotor core 86 and the permanent magnet 88. A permanent magnet guider 201 is formed at an interior circumference of the rotor cover 84 such that movement of the permanent magnet 88 mounted at the rotor core 86 along the central axis x is restricted. Therefore, the rotor cover 84 primarily fixes the rotor core 86 and the permanent magnet 88, and is made of copper or stainless steel that has high specific gravity. In addition, the rotor cover 84, as shown in FIG. 7, is formed of a plurality of balance holes 205. If the rotor 200 is manufactured, it is checked whether the rotor 200 is rotationally balanced. If the rotor 200 is not rotationally balanced, noise or vibration may occur when the water pump 1 operates. Thereby, performance of the water pump 1 may be deteriorated. Therefore, positions of the balance holes 205 are changed such that the rotor 200 is rotationally balanced.

In a state in which the rotor core 86 and the permanent magnet 88 are mounted to the rotor cover 84, the rotor case 90 wraps exterior circumferences of the rotor core 86 and the permanent magnet 88 so as to secondarily fix them. The rotor case 90 is made of a bulk mold compound (BMC) including a potassium family that has a low coefficient of contraction. A method for manufacturing the rotor case 90 will be briefly described.

The rotor core 86 and the permanent magnet 88 are mounted to the rotor cover 84, and the rotor cover 84 to which the rotor core 86 and the permanent magnet 88 are mounted is inserted in a mold (not shown). After that, the bulk mold compound including the potassium family is melted and high temperature (e.g., 150° C.) and high pressure BMC is flowed into the mold. Then, the BMC is cooled in the mold. As described above, if the rotor case 90 is made of BMC having the low coefficient of contraction, the rotor case 90 can be precisely manufactured. In general, the coefficient of contraction of a resin is 4/1000-5/1000, but the coefficient of contraction of the BMC is about 5/10,000. If the rotor case 90 is manufactured by flowing the high temperature resin into the mold, the rotor case 90 is contracted and does not have a target shape. Therefore, if the rotor case 90 is manufactured by the BMC including the potassium family that has the low coefficient of contraction, contraction of the rotor case 90 by cooling may be reduced and the rotor case 90 may be precisely manufactured. In addition, since BMC including the potassium family has good heat-radiating performance, the rotor can be cooled independently. Therefore, the water pump 1 may be prevented from being heat damaged.

In addition, according to a conventional method for manufacturing the rotor, the permanent magnet is fixed to the exterior circumference of the rotor core with glue. However, as the rotor rotates, high temperature and high pressure are generated near the rotor. Thereby, the glue may be melted or the permanent magnet may be disengaged from the rotor core. The permanent magnet 88 mounted to the rotor core 86, on the contrary, is fixed primarily by the rotor cover 84 and secondarily by the rotor case 90 according to an exemplary embodiment of the present invention. Thus, the permanent magnet 88 may not be disengaged from the rotor core 86.

The stator chamber 42 is formed in the body 30 at a radially outer portion of the rotor chamber 38. The stator 101 is mounted in the stator chamber 42.

The stator 101 is fixed to the body 30 directly or indirectly, and includes a stator core 102, an insulator 104, a coil 108, and a stator case 109.

The stator core 102 is formed by stacking a plurality of pieces made of a magnetic material. That is, the plurality of thin pieces is stacked up such that the stator core 102 has a target thickness.

The insulator 104 connects the pieces making up the stator core 102 to each other, and is formed by molding a resin. That is, the stator core 102 formed by stacking the plurality of pieces is inserted in a mold (not shown), and then molten resin is injected into the mold. Thereby, the stator core 102 at which the insulator 104 is mounted is manufactured. At this time, coil mounting recesses 106 are formed at front and rear end portions of the stator core 102 and the insulator 104.

The coil 108 is coiled at an exterior circumference of the stator core 102 so as to form a magnetic path.

The stator case 109 wraps and seals the stator core 102, the insulator 104, and the coil 108. The stator case 109, the same as the rotor case 90, is manufactured by insert molding the BMC including the potassium family.

In addition, when the stator case 109 is insert molded, a Hall sensor 112 and a Hall sensor board 110 may also be insert molded. That is, the stator 101, the Hall sensor 112, and the Hall sensor board 110 may be integrally manufactured as one component.

The Hall sensor 112 detects the position of the rotor 200. A mark (not shown) for representing the position thereof is formed at the rotor 200, and the Hall sensor 112 detects the mark in order to detect the position of the rotor 200.

The Hall sensor board 110 controls a control signal delivered to the stator 101 according to the position of the rotor 200 detected by the Hall sensor. That is, the Hall sensor board 110 makes a strong magnetic field be generated at one part of the stator 101 and a weak magnetic field be generated at the other part of the stator 101 according to the position of the rotor 200. Thereby, initial mobility of the water pump 1 may be improved.

A case mounting portion 46 is formed at an exterior surface of the rear end of the body 30.

The driver case 50 is engaged to the rear end of the body 30, and is formed of a case surface 52 at a front end portion thereof. The rotor chamber 38 and the stator chamber 42 are formed in the body 30 by engaging the driver case 50 to the rear end portion of the body 30. A body mounting portion 60 is formed at an external circumference of the front end portion of the driver case 50 and is engaged to the case mounting portion 46 by fixing means such as a bolt B.

The case surface 52 is provided with an insert portion 54, a second stator mounting surface 56, and a second bearing mounting surface 58 formed sequentially from an exterior circumference to a center thereof.

The insert portion 54 is formed at an external circumferential portion of the case surface 52 and is protruded forward. The insert portion 54 is inserted in and closely contacted to the rear end portion of the body 30. Sealing means such as an O-ring O is interposed between the insert portion 54 and the rear end portion of the body 30 so as to close and seal the stator chamber 42.

The second stator mounting surface 56 is protruded forward from the case surface 52 so as to define the boundary between the stator chamber 42 and the rotor chamber 38. The rear end of the stator 101 is mounted at the second stator mounting surface 56 with a sealing means such as an O-ring O being interposed. The stator chamber 42 is not fluidly connected to the rotor chamber 38 by the O-ring O interposed between the first stator mounting surface 40 and the front end of the stator 101 and the O-ring O interposed between the second stator mounting surface 56 and the rear end of the stator 101. Therefore, the coolant having flowed in the rotor chamber 38 does not flow to the stator chamber 42.

The second bearing mounting surface 58 is protruded forwardly from the case surface 52. A second bearing 96 is interposed between the second bearing mounting surface 58 and the rear end portion of the shaft 82 so as to make the shaft 82 smoothly rotate and to prevent the shaft 82 from being inclined.

The rear end of the driver case 50 is open. The driver chamber 64 is formed between the driver case 50 and the driver cover 70 by engaging the driver cover 70 of a disk shape to the rear end of the driver 50 by fixing means such as a bolt B. For this purpose, a protruding portion 72 is protruded forward from an exterior circumference of the driver cover 70, and this protruding portion 72 is inserted in and closely contacted to an exterior circumference 62 of the rear end of the driver case 50. Sealing means such as an O-ring O is interposed between the protruding portion 72 and the exterior circumference 62 so as to prevent foreign substances such as dust from entering the driver chamber 64.

The driver 80 controlling operation of the water pump 1 is mounted in the driver chamber 64. The driver 80 includes microprocessors and a printed circuit board (PCB). The driver 80 is electrically connected to a controller (not shown) disposed at an exterior of the electric water pump 1 through a connector 74 and receives a control signal of the controller. In addition, the driver 80 is electrically connected to the Hall sensor board 110 so as to transmit the control signal received from the controller to the Hall sensor board 110.

Meanwhile, the driver chamber 64 is isolated from the rotor chamber 38 by the case surface 52. Therefore, the coolant in the rotor chamber 38 does not flow into the driver chamber 64.

Hereinafter, the stator 101 of the electric water pump 1 according to an exemplary embodiment of the present invention will be described in further detail with reference to FIG. 3.

FIG. 3 is a perspective view showing a stator of an electric water pump according to an exemplary embodiment of the present invention.

As shown in FIG. 3, a plurality of fixing grooves 105 are formed at the external circumference of the rear end of the stator case 109. The insert portion 54 is inserted in the fixing groove 105 so as to limit rotational and axial movements of the stator 101 according to the rotation of the rotor 200. Such a fixing groove 105 can be formed together with the stator case 109 when the stator case 109 is insert molded, and an additional process or an additional device is not required for forming the fixing groove 105. Therefore, processes for manufacturing the stator 101 do not increase. In addition, since the stator 101 is fixed to the body 30 neither with glue nor by press-fitting, the stator 101 can be easily disassembled from the body 30. Therefore, if the stator 101 is out of order, the stator 101 can be easily replaced.

In addition, as shown in FIG. 2, the interior circumference of the stator case 109 forms a part of the rotor chamber 38. As described above, the coolant flows into the rotor chamber 38 and moves in the rotor chamber 38 by rotation of the shaft 82 and the rotor 200. Since a stator groove 122 is formed at the interior circumference of the stator case 109 along the length direction thereof, the coolant in the rotor chamber 38 flows along the stator groove 122 and removes floating materials attached to the interior circumference of the stator case 109. The shape of the stator groove 122 can be easily determined by a person of ordinary skill in the art considering the flow of the coolant in the rotor chamber 38.

Further, in order to reduce vibration and noise according to the rotation of the rotor 200 and to reduce vibration generated when a vehicle drives, a plurality of damping holes 120 are formed at the stator case 109. Vibration and noise according to the rotation of the rotor 200 and vibration generated when the vehicle drives are absorbed by movement of gas in the stator chamber 42 through the damping hole 120. The position and shape of the damping hole 120 can be easily determined by a person of ordinary skill in the art according to vibration frequency and pressure frequency of the stator 101. In addition, a frothing resin or sound absorbing material may be filled in the damping hole 120 so as to further reduce vibration and noise.

Meanwhile, the stator groove 122 and the damping hole 120 may be formed at the rotor 200. That is, grooves (not shown) may be formed at the exterior circumference of the rotor case 90 such that the coolant in the rotor chamber 38 flows along the grooves and removes the floating materials attached to the exterior circumference of the rotor case 90. In addition, vibration and noise according to the rotation of the rotor (84, 86, 88, and 90) and vibration when the vehicle drives may be absorbed by forming holes (not shown) at the rotor case 90.

FIG. 7 is a schematic diagram showing processes for manufacturing a rotor used in an electric water pump according to an exemplary embodiment of the present invention.

If the rotor core 86 provided with the plurality of recesses 203 at the exterior circumference thereof is provided as shown in FIG. 7A, the permanent magnets 88 are inserted in each recess 203 as shown in FIG. 7B. At this time, the permanent magnets 88 are mounted in such the manner that the N pole and the S pole are alternately disposed.

After that, the rotor covers 84 are mounted at both ends of the rotor core 86 and the permanent magnet 88 as shown in FIG. 7C. Thereby, the permanent magnets 88 are primarily fixed to the rotor core 86.

After that, the rotor case 90 is molded to the exterior circumference of the rotor core 86 and the permanent magnet 88 as shown in FIG. 7D.

When the rotor 200 is manufactured as described above, it is checked whether the rotor 200 is rotationally balanced. If the rotor 200 is not rotationally balanced, the positions of the balance holes 205 are determined in order to keep the rotational balance of the rotor 200. Then, the balance holes 205 are formed at the rotor cover 84.

Since a stator and a rotor that are electrically operated are wrapped by a resin case having waterproof performance according to an exemplary embodiment of the present invention, performance and durability of an electric water pump may improve.

In addition, since a Hall sensor and a Hall sensor board are mounted in the stator and a control signal is changed according to an initial position of the rotor, initial mobility of the electric water pump may improve.

Further, the shape of the rotor core may be optimized so as to minimize leakage of magnetic flux of the permanent magnet. Therefore, sufficient capacity of the water pump may be achieved without increasing the size of the water pump.

For convenience in explanation and accurate definition in the appended claims, the terms “interior”, “exterior”, “inner”, and “outer” are used to describe features of the exemplary embodiments with reference to the positions of such features as displayed in the figures.

The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents. 

1. An electric water pump apparatus comprising: a stator generating a magnetic field according to a control signal; and a rotor enclosed by the stator and rotated by the magnetic field generated at the stator to pressurize coolant, wherein the rotor includes: a rotor core having a hollow cylindrical shape to receive a shaft therein, and provided with a plurality of recesses formed by a plurality of guiding protrusions formed at an exterior circumference thereof along a length direction; a plurality of permanent magnets respectively mounted in the plurality of recesses of the rotor core; a rotor cover mounted at both distal ends of the rotor core and the plurality of permanent magnets so as to fix the rotor core and the plurality of permanent magnets each other; and a rotor case enclosing an exterior circumference of the rotor core and the plurality of permanent magnets so as to fix the rotor core and the plurality of permanent magnets each other in a state that the rotor core and the plurality of permanent magnets are mounted at the rotor cover.
 2. The electric water pump apparatus of claim 1, wherein the rotor core includes a coupling groove formed along an inner circumference of the rotor core and the rotor core is splined to the shaft through the coupling groove.
 3. The electric water pump apparatus of claim 1, wherein the plurality of permanent magnets is mounted in such a manner that N pole and S pole are alternately disposed each other.
 4. The electric water pump apparatus of claim 1, wherein the rotor case is made of a bulk mold compound including a potassium family that has a low coefficient of contraction.
 5. The electric water pump apparatus of claim 1, wherein the rotor cover is provided with at least a balance hole and rotational balance of the rotor is adjusted by locations and number of the at least a balance hole.
 6. The electric water pump apparatus of claim 1, wherein the stator includes: a stator core having a hollow cylindrical shape to receive the rotor therein and provided with a stator groove at an inner circumference thereof along a length direction; and a stator case mounted at both distal ends of the stator core.
 7. The electric water pump apparatus of claim 6, wherein the stator case is made of a bulk mold compound including a potassium family that has a low coefficient of contraction.
 8. The electric water pump apparatus of claim 6, wherein the stator case is provided with at least a balance hole such that rotational balance of the stator is adjusted by locations and number of the at least a balance hole.
 9. The electric water pump apparatus of claim 6, wherein the stator case is provided with a fixing groove and a driver providing the control signal is slidably and detachably coupled thereto.
 10. An electric water pump apparatus comprising: a stator generating a magnetic field according to a control signal; a rotor enclosed by the stator and rotated by the magnetic field generated at the stator; a pump cover having an inlet through which coolant flows in and an outlet through which pressurized coolant flows out; a body having: a front surface forming a volute chamber between the pump cover and the front surface; a stator chamber formed at an outer portion of the body in a radial direction and the stator being mounted in the stator chamber; and a rotor chamber formed at an inner portion of the body in a radial direction, and the rotor being mounted in the rotor chamber, wherein the stator fluidly insulates the rotor chamber and the stator chamber therebetween; a shaft having a central axis, fixed to the rotor so as to rotate together with the rotor about the central axis, and mounted in the rotor chamber; an impeller fixed to a front portion of the shaft so as to rotate together with the shaft, pressurizing the coolant having flowed in through the inlet, and mounted in the volute chamber; a driver case detachably mounted at a rear end of the body, formed of a case surface at a front surface thereof, having a rear surface opened backward, and formed of a driver chamber therein; and a driver mounted in the driver chamber and applying a control signal to the stator, wherein the rotor comprises a rotor core having a hollow cylindrical shape, and provided with a plurality of recesses formed by a plurality of guiding protrusions formed at an exterior circumference thereof along a length direction, a plurality of permanent magnets respectively mounted in the plurality of recesses of the rotor core, a rotor cover mounted at both distal ends of the rotor core and the plurality of permanent magnets so as to fix the rotor core and the plurality of permanent magnets each other, and a rotor case enclosing an exterior circumference of the rotor core and the plurality of permanent magnets so as to fix the rotor core and the plurality of permanent magnets each other in a state that the rotor core and the plurality of permanent magnets are mounted at the rotor cover.
 11. The electric water pump apparatus of claim 10, wherein the rotor case is made of a bulk mold compound including a potassium family that has a low coefficient of contraction.
 12. The electric water pump apparatus of claim 10, wherein the rotor cover is provided with at least a balance hole and rotational balance of the rotor is adjusted by changing locations and numbers of the at least a balance hole.
 13. An electric water pump apparatus comprising: a body having a hollow cylindrical shape and including a stator chamber and a rotor chamber therein; a stator having a hollow cylindrical shape and being disposed in the stator chamber and generating a magnetic field according to a control signal, wherein the stator fluidly insulates the stator chamber and the rotor chamber, a rotor disposed in the rotor chamber and enclosed by the stator, wherein the rotor is rotated by the magnetic field generated at the stator; and a pump cover connected to the body and forming a volute chamber therein, wherein the volute chamber and the rotor chamber are fluidly-communicated through a connecting hole formed to the body and a coolant having flowed into the volute chamber is supplied to the rotor chamber through the connection hole, wherein the stator includes a stator groove formed in an inner circumference therein and the stator groove is fluid-connected to the rotor chamber and the volute chamber through the connection hole.
 14. The electric water pump apparatus of claim 13, wherein the rotor core having a hollow cylindrical shape includes a coupling groove formed along an inner circumference in a length direction therein and the rotor core is splined to the shaft through the coupling groove.
 15. The electric water pump apparatus of claim 13, wherein the stator includes: a stator core having a hollow cylindrical shape to receive the rotor therein and provided with the stator groove at an inner circumference thereof along a length direction; and a stator case mounted at both distal ends of the stator core.
 16. The electric water pump apparatus of claim 15, wherein the stator case is made of a bulk mold compound including a potassium family that has a low coefficient of contraction.
 17. The electric water pump apparatus of claim 15, wherein the stator case is provided with a fixing groove and a driver providing the control signal is slidably and detachably coupled thereto.
 18. The electric water pump apparatus of claim 13, wherein the rotor includes: a rotor core having a hollow cylindrical shape to receive a shaft therein, and provided with a plurality of recesses formed by a plurality of guiding protrusions formed at an exterior circumference thereof along a length direction; a plurality of permanent magnets respectively mounted in the plurality of recesses of the rotor core; a rotor cover mounted at both distal ends of the rotor core and the plurality of permanent magnets so as to fix the rotor core and the plurality of permanent magnets each other; and a rotor case enclosing an exterior circumference of the rotor core and the plurality of permanent magnets so as to fix the rotor core and the plurality of permanent magnet each other in a state that the rotor core and the plurality of permanent magnets are mounted at the rotor cover.
 19. The electric water pump apparatus of claim 18, wherein the rotor case is made of a bulk mold compound including a potassium family that has a low coefficient of contraction. 